This invention pertains to packaging. It pertains in some respects to compositions of matter and single layer polymeric films made therefrom, and in other respects to multiple layer sheet materials and packages made therefrom. The sheet materials may be entirely polymeric, or they may include non-polymeric components. The multiple layer materials may be flexible, or relatively rigid. The invention also pertains to processes for making packaging materials. This invention is especially concerned with packaging sheet materials which are formed into packages.
Various packaging applications wherein a produce is packaged in a heat sealable sheet material require that the finished package be able to withstand substantial abuse, such as in shipping and handling. In some packaging applications, the package, including the packaging materials and the product being packaged, may be subject to certain process treatments either during or after the filling and sealing of the package. One such application is retortable packages, where the package is subjected to sterilizing conditions of typically about 250.degree. F., and appropriate respective pressures for steam sterilization, typically for periods of 30-60 minutes, but sometimes as little as 10 minutes is acceptable.
A multiplicity of packaging materials have been developed for use in heat seal-type packaging. While many of these packaging materials have experienced a degree of success, there remain problems in packages which are subject to certain abuses related to their use. Particularly, packages containing liquid products experience hydraulic pressure exerted by the liquid product when they receive physical shocks such as when dropped, or moved in a rough manner. Where the shock is sufficiently strong, the heat seals may break as a result. And while certain sheet structures are in conventional use, it is desirable to make improved economical sheet structures which can be used to make even stronger packages, and particularly, stronger package sealant layers and seals, to further reduce the incidence of failure of the filled and sealed package. Packaging materials which have been subjected to high temperature processing are particularly susceptible to breakage of the package seals.
Particularly referring, now to packages which are subjected to thermal processing, as in retort processing typically at about 250.degree. F., sealant layers are known to be made of polypropylene, as in U.S. Pat. No. 4,190,477. While polypropylene sealant layers are functionally capable of withstanding the processing conditions, the heat seals, as measured after processing, could desirably be stronger.
It is an object of this invention to provide novel packaging sheet materials.
It is another object of the invention to provide novel multiple layer sheet materials having improved capability to withstand physical shocks when formed into flexible heat sealed packages filled with liquid, and packages made from those sheet materials.
It is still another object to provide such novel sheet materials having good barrier to transmission of gases or moisture into or out of the package.
It is yet another object to provide novel sheet materials capable of withstanding substantial physical shocks when formed into flexible heat sealed packages filled with liquid; the packages having good barrier to transmission of gases or moisture; and the packages having sufficient optical clarity through the sheet material to enable visual inspection of the package contents; and packages made from those sheet materials.
Further objects are in process for making the improved sheet materials of the invention, and the package made therefrom.